1. Field of the Invention
This invention relates generally to systems for advising the pilot of a vehicle such as an aircraft or a submarine of the proximity of obstacles or terrain in the path of the vehicle, and more particularly to a system that utilizes navigationally derived position data as well as barometric and radio altitude and rate data, glide slope signals and other flight parameters, and issues an advisory or a warning to the pilot in the event of a hazardous flight condition.
2. Description of the Prior Art
Various systems that provide warnings or advisory indications in the event of hazardous flight conditions are known. Among such systems are systems generally known as ground proximity warning systems for aircraft that serve to monitor the flight conditions of an aircraft and provide a warning if flight conditions are such that an inadvertent contact with the ground is imminent. Among the flight conditions monitored by such systems are radio altitude and rate, barometric altitude and rate, airspeed, and flap and gear positions. The aforementioned parameters are monitored, and an advisory indication or a warning is generated when the relationship between the aforementioned conditions or parameters is such that ground impact is likely to occur. Typical examples of such systems are disclosed in U.S. Pat. Nos. 3,715,718, 3,936,796, 3,958,218, 3,944,968, 3,947,808, 3,947,810, 3,934,221, 3,958,219, 3,925,751, 3,934,222, 4,060,793, 4,030,065, 4,215,334 and 4,319,218, all assigned to the same assignee as the assignee of the present invention.
While the above-described systems provide advisory and warning signals in the event of proximity to terrain, such systems generate warnings based solely on the flight conditions of the aircraft, and do not utilize navigation information. Consequently, the sensitivity of such systems must be adjusted to provide adequate warnings when a hazardous flight condition exists without generating false or nuisance warnings when there is no danger. Such an adjustment results in a comprise that may still cause nuisance warnings when flying over terrain unique to particular geographic areas, and shorter than desired warning times in other geographic areas.
One attempt to correct some of the above-described disadvantages has been to modify the warning envelopes of the ground proximity warning system in accordance with the geographic location of the aircraft in order to optimize the warning criteria for the particular geographic area over which the aircraft is flying. An example of such a system is described in U.S. patent application Ser. No. 448,862, now U.S. Pat. No. 4,567,483, filed Dec. 10, 1982 by Bateman, et al. and assigned to the same assignee as the assignee of the present invention. In the system disclosed in the aforesaid application, the warning criteria are optimized to suit the terrain characteristics about certain limited areas, particularly the characteristics of particular airports where nuisance warnings and other problems have been encountered. However, due to the logic utilized, the amount of area defining data that can be stored and manipulated is limited.
Another approach utilizing a geographical input is used in U.S. Pat. No. 4,224,669. In the system disclosed in the aforesaid patent, a memory device is employed to store minimum safe altitudes by geographic coordinate areas. A navigational computer is used to determine the position of the aircraft, and a warning is given if the aircraft descends below the stored minimum safe altitude for the coordinate area in which the aircraft is flying. The system has a "worst case" and a "tactical" mode of operation. In the "worst case" mode, the minimum safe altitude is determined as a function of the highest terrain feature or obstacle within the geographic coordinate area of interest. In the "tactical" mode of operation, current flight conditions such as position, ground speed and ground track are used to define a minimum safe altitude based on the height of terrain and obstacles immediately ahead of the projected flight path.
While these systems do provide warning of the proximity of terrain or obstacles, the system described in the aforesaid Bateman application only provides optimized warning criteria for a few areas, particularly airports, and still utilizes compromise type warning criteria in most other areas. The system described in U.S. Pat. No. 4,224,669 simply defines a minimum altitude based on the operating conditions of the aircraft and its location, rather than providing a warning when the interrelationships between various flight parameters are such that a hazardous flight condition is indicated.